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RAF Riccall, near Cawood in North Yorkshire, was created for a specific and highly demanding purpose: heavy bomber conversion. Opened in September 1942 as part of Bomber Command’s training and conversion system, it became associated with No. 1658 Heavy Conversion Unit (HCU). HCUs were where crews already trained on twin-engined aircraft learned to operate four-engined heavies, mastering the handling, systems and crew procedures required for combat operations in aircraft such as the Handley Page Halifax.
Riccall’s formation history reflects wartime urgency. As Bomber Command expanded, conversion flights and squadron conversion elements were brought together to create a dedicated unit. Multiple Halifax conversion flights and elements linked to squadrons such as Nos. 10, 76, 78, 102 and 158 were among those involved in the creation of 1658 HCU at Riccall, producing a concentrated training capability. This mattered because heavy bomber operations depended on crews who could manage complex aircraft at night, in formation, under strict procedure, and often in poor weather. A small mistake on a four-engined type could be catastrophic; the conversion unit’s job was to reduce that risk before crews reached the front line.
The principal aircraft at Riccall was the Halifax, including early operational variants used for training. The Halifax demanded skills in engine management, asymmetric handling, long take-offs at heavy weights, and precise instrument flying. At the same time, crews practised navigation, bombing procedures and gunnery coordination to the extent possible within the conversion context. Because conversion flying involved repeated circuits, cross-countries and emergency drills, it carried its own hazards. Accidents and forced landings occurred, and the station’s history includes incidents where operational crews diverted in bad weather and landed at Riccall, highlighting how Yorkshire’s airfields functioned as a network of alternates for one another.
Riccall’s role changed as the war moved on. In April 1945, the station’s conversion function transferred away as priorities shifted towards transport and post-war reorganisation. Yet the core wartime significance remains clear: Riccall was a ‘gateway’ station. Airmen who passed through 1658 HCU went on to front-line Halifax units and other heavy bomber squadrons, carrying with them the practical skills and procedural habits learned at Riccall. In this sense, the airfield is part of the hidden scaffolding of the bomber offensive – an essential step between training and combat that enabled Bomber Command to sustain operations at scale.
Today, RAF Riccall is remembered primarily through that conversion role and its connection to the Halifax. For researchers, it also offers a way to understand the geography of Bomber Command’s Yorkshire bases: operational stations, satellites, training fields and conversion units all interlocking to produce a continuous flow of aircraft and crews.
WW2 units, roles and aircraft:
- No. 1658 Heavy Conversion Unit (HCU) – heavy bomber conversion training
- Primary aircraft: Handley Page Halifax (training on operational variants)
- Linked conversion elements: Halifax conversion flights associated with multiple Bomber Command squadrons (including Nos. 10, 76, 78, 102, 158)
Because conversion training demanded repetition, Riccall also influenced aircraft reliability and crew confidence. By encountering engine failures, navigation problems and bad-weather approaches in a controlled setting, crews learned to manage emergencies before facing combat. The station’s legacy is therefore embedded in the survival skills carried forward into operational squadrons.